The present invention relates to a detection method of the interval variation of recorded positions printed by plural recording elements.
Recently, as in an inkjet recording head in which plural nozzles are aligned, used is a recording head in which plural recording elements are aligned. A single recording head is used, or the plural heads are aligned and used to increase the scanning width. These recording elements function as an element which prints a minimum unit of a printed image, similar to the nozzle of an inkjet printer.
Whichever may be used, whether a single recording head or plural aligned recording heads, high uniformity of the interval pitch of the recorded positions printed by the recording elements is required for the targeted quality of printed matters.
The uniformity of pitch of the positions recorded by the recording elements of the single head depends upon the manufacturing accuracy of the recording head. For example, when the recorded positions of each recording element in the single head vary about “±a” μm compared to the ideal position, and an ideal pitch interval is “P” μm, then the interval of the recorded position printed by said head is set within (P±a) μm.
When the plural recording heads are aligned for use, the high uniformity of pitch, including any joints of adjacent recording heads, is very important not only for the print targeting high dimensional printing accuracy, but also for industrial production wherein colored materials of a liquid-crystal color filter or a light emitting element of an organic EL is precisely coated within a microscopic cell. When the plural recording heads are aligned, the accuracy of the pitch between adjacent recording heads depends upon the configurational accuracy of the recording heads. Therefore, detection methods of the relative position of the recording heads have been recently proposed.
In the invention of Patent Document 1, the recording heads are positioned to overlap each other so that several nozzles on both ends of the recording head are subjected to print a pattern, and thereby, the relative position of the adjacent recording heads were detected.
In the invention of Patent Document 2, the recording heads are positioned to overlap each other so that as a sensor reads an image, the relative position of the adjacent recording heads were detected.
The invention of Patent Document 3 concerns a technology to detect inclination of the recording head in the main scanning direction, while the invention of Patent Document 4 concerns a technology to detect parallelism of plural spliced recording heads, which cannot detect the pitch of the recorded position on a joint of adjacent recording heads.
[Patent Document 1] JP-A 2002-79657
[Patent Document 2] JP-A 2002-96462
[Patent Document 3] JP-A 10-115955
[Patent Document 4] JP-A 2003-170645
The problems described below were noted in the above-mentioned conventional technologies.
Now, a simplified model, shown in FIGS. 6-8, is being studied. In FIG. 6, recording elements n1-n7 are aligned in recording head H1, while recording elements n8-n14 are aligned in recording head H2. Recording elements n1-n14 (total 14 elements) are arranged at an equal pitch in perpendicular direction to main scanning direction X. The pitch being studied is evaluated based on the recorded position on a recording media. For example, when the recording element is a nozzle, the pitch is evaluated based on the deposited position of ink droplets jetted from the nozzles onto the recording media, and not evaluated for the aligned pitch of the nozzles themselves. FIG. 6 shows the ideal condition in which recorded patterns 1-14 are printed by recording elements n1-n14 at equal pitch P.
Next, the case in FIG. 7 will be discussed. Recorded pattern 8 is deviated toward recorded pattern 9 by distance “a” compared to the ideal pitch line (shown by a dotted line), while recorded pattern 14 deviates in the opposite direction by distance “a”.
If the positional deviations shown in FIG. 7 are detected by the invention of Patent Document 1 or 2, deviated amount “a” is detected as the relative position of the adjacent recording heads, therefore, recording heads H1 and H2 are to be repositioned with the gap between recording heads H1 and H2 reduced by “a” as shown in FIG. 8. Then, recorded patterns 9-13 recorded by recording head H2 are deviated by distance “a” from the ideal pitch patterns (shown by the dotted lines). Accordingly, recorded pattern 14 is deviated from the ideal pitch pattern by distance “2a”. This is because the relative position of the adjacent recording heads is decided based on recorded pattern 8 being deviated at distance “a” as a specific characteristic of the recording head, and thereby, the positions of recorded patterns 9-14 via recording elements n9-n14 are additionally deviated by distance “a”.
In a case that the positions of each of recorded patterns 1-14 are optionally varied within the scope of “P ±a” μm, the maximum error of “2a” is generated by the reposition the recording head. Further, it is understood that any one of the recorded patterns may have an error greater than “a”. This means that when there is an allowable error of ±“a” μm, even though the formation of each recording head are within the allowable error, the error, being greater than the allowable error of the recording heads, is generated by defective positioning process of the recording heads.
This error may not have a large negative influence on the image quality during printing, however, in the case that a material is given within a microscopic area, as in the case that color materials of a liquid-crystal color filter or a light emitting element of an organic EL is positively coated within a microscopic cell, deformities may be generated such as an “image dropout”, which cannot satisfy the desired quality.
In FIGS. 6 and 7, recording heads H1 and H2 are used on for explanation, but if the number of the recording heads is increased to H1, H2, H3 - - - (each is not illustrated), which would of course increase the number of arrays of the recording elements, whereby the error at subsequent joints accumulates, and recording elements of the recording head at the far end may be positioned by a deviated amount far greater than “2a”.
Accordingly, the more the number of recording heads which are combined, the more difficult is to satisfy the desired characteristic, being unable to satisfy the required quality.
Further, if the detection of positional deviation shown in FIG. 8 is tried by the invention of Patent Document 1 or 2, it is not possible to detect deviated amount “a” of recorded patterns 9-13, which are not targeted, nor deviated amount “2a” of recorded pattern 14 at the end, not being a joint.
According to the conventional art in which the sensor is employed for the detection, in order to adjust the recorded positions recorded by each recording element within the tolerance, each error of the recorded positions recorded by each recording element must be detected.
In addition, in order to reduce the pitch, the recording elements of each recording head may be arranged at an angle in scanning direction X as shown in FIG. 9, however, this case also has the same problem as mentioned above.
The present invention has been achieved in view of the above-cited conventional technology. A target of the present invention is to provide the method which is able to easily detect all of the interval changes of the recorded positions which are recorded by plural arrays of recording elements, each structured in a recording head, as well as the recording apparatus which is able to detect the interval of recorded position recorded by the plural recording heads mounted therein.